You can see that if you know these rules most of the problems are easy to answer. However, white below does not mean it is hard. It just means that problem is not covered by one of the seven rules. Take a look at the white ones below. You may already know several of them.
You can also combine rules and figure out the answer to the white ones.
Let’s look at the example 9 X 12. Pretend you don’t know the answer. If you know 9 X 11 = 99 (Rule 5) and you know that multiplication is simply repeated addition(Before You Begin), then then you will know 9 X 12 = 99 + 9 = 108. Easy!
Now that you know the rules all you need to do is practice.